1. Field of Invention
This invention relates to a new method and apparatus for the rearing and maturing of oyster seed stocks and other molluscs through aquaculture in off-bottom, corrosion-proof, freely movable cradles which support foraminous trays or cribs of varying mesh sizes containing cultchless young oysters at different growth stages.
2. Prior Art Relating to the Disclosure
The reproductive cycle of the oyster in its natural state usually centers in areas of acceptable water environment where reefs or beds of oysters can develop on firm bottom substrate and successively spawn free-swimming larvae which attach themselves to the shells of their predecessors and grow to maturity. The protein food value of oysters, and the relative simplicity of concentrating their self-renewing production capabilities in properly selected growth environments, led originally to the development of culture techniques in the early years of the Roman Empire. These were extended to, and adapted in many parts of Western Europe and the British Isles in succeeding centuries. Oyster meats were a prime source of protein for mass urban consumption in the Elizabethan era, for example, and one mainstay of the U.S. East Coast seafood diet in the mid-Atlantic coastal areas during the late 19th and early 20th centuries.
Beginning in the 1930's, when domestic and foreign oyster production began to fall off rapidly due variously to pollution, diseases, unanticipated new forms of predation, and destruction of natural bed areas as well as nutrient source wetlands, a number of research programs were undertaken in the U.S.A. and elsewhere to reverse the lowering production trends for edible shellfish. Remedies were sought in two broad areas:--by studies of the "natural" breeding and growth problems and developing corrective measures and techniques therefor, and by introducing systems for "aquaculture", which has since become a term generally used to describe off-bottom culture methodologies. In this latter field, innovations followed several different patterns. Rafts or floats were used to suspend ropes and shellfish shell strings to permit naturally spawned larvae to attach themselves to a cultch or artificial bed regardless of actual bottom conditions at the sites. Hatchery techniques were developed to produce cultchless (separately nutured) oyster seed which could be grown in foraminous trays suspended off-bottom under rafts. These and other aquaculture concepts projected widespread extension of water areas suitable for oyster production, substantial reduction of predation, uniform shell growth and size etc. The techniques developed to achieve these objectives have, so far, proved relatively costly to apply, however, and private enterprise capital has not yet been significantly attracted to shellfish aquaculture as a profitable way to exploit those potentially massive renewable marine resources in many of the coastal and estuarine areas of the U.S.